Almost any peripheral hearing loss results in some atrophic effects of auditory portions of the brainstem. The proposed morphological experiments will use experimental mice and guinea pigs to determine: 1) If the dendrites of ventral cochlear neurons are adversely affected by neonatal auditory deprivation, neonatal conductive losses, and/or neonatal cochlear removal; 2) If there is a direct correlational relationship between cochlear atrophy and ventral cochlear nuclear atrophy in deafness mice (dn/dn); 3) If ganglioside tratment can ameliorate transneuronal atrophy in hearing impaired mice and guinea pigs; 4) If there are quantitative and/or qualitative differences in the cochlear nuclei of mice with long-term cochlear removals starring neonatally as compared to those starting in adult mice; and 5) If there are dramatic short-term effects of cochlear removals in mice as there are in chicks. The results of these experiments will document the age-dependent, transneuronal, atrophic effects of peripheral hearing impairments and explore means of ameliorating them.